In the automatic analysis apparatus, circulated water stored in a reaction vessel and light which has passed through the object to be measured are measured. Therefore, when foreign substances such as forms and dusts are mixed into the circulated water in the reaction vessel, a noise is detected since the light is scattered by the foreign substances. Then, the noise affects the measurement results.
To remove the foreign substances, for example, it is necessary to replace water in the reaction vessel once in every 24 hours as a maintenance operation.
PTL 1 discloses a technique for removing foams in thermostatic bath water as a method for removing the foreign substances.